The objective of the study was to evaluate the visual assessment of vaginal discharge by vaginoscopy for the diagnosis of clinical endometritis (CE) in dairy cows. In an in vivo trial, inter- and intraobserver repeatability of vaginoscopic examination (VE) was determined and the effect of transrectal palpation and experience of the investigator evaluated. Holstein-Friesian cows (n=380) were examined by vaginoscopy between 21 and 27 d in milk by 3 investigators twice. Vaginal discharge was categorized on a 4-point classification system (0=clear mucus, 1=mucus containing flecks of pus, 2=discharge containing less than 50% pus, 3=discharge containing more than 50% pus). Cows with a vaginal discharge score (VDS) of 0 were classified as healthy, whereas cows with a VDS of 1 to 3 were classified as having CE. Vaginal discharge score on a scale from 0 to 3 has moderate intra- (Cohen's kappa coefficient, κ=0.55-0.60) and interobserver (κ=0.44) repeatability. The prevalence of CE was comparable between the 3 investigators (first VE: 42.6, 34.8, and 38.7; second VE 46.8, 36.9, and 43.7%). Transrectal palpation (relative risk=0.96-1.03) or experience of the investigator (relative risk=0.9-1.1) did not affect results of VE. In an in vitro trial, sensitivity and specificity of visual assessment were determined utilizing 33 images showing yellow and pink areas in certain percentages as a reference standard. Pus was represented by yellow areas and the mucosa, including clear mucus, by pink areas. These images were visually assessed by 30 investigators via PowerPoint presentation (experiment 1) and by 23 investigators via a simulated vaginal examination (experiment 2) utilizing the same 4-point classification system. Sensitivity was 99.6 and 96.3% and specificity was 96.7 and 90.1% in experiments 1 and 2, respectively. The results provide evidence that a visual assessment conducted by vaginoscopic examination is not perfect but can be considered a reasonable measurement of vaginal discharge and is a practical tool to distinguish healthy from diseased cows.